This invention is related to the field of processes for producing a polymer composition.
The production of polymers is a multi-billion dollar business. This business produces billions of pounds of polymers each year. Millions of dollars have been spent on developing technologies that can add value to this business.
Increasing production of polymers from polymerization processes is an important area of polymer research. In addition, discovering new polymer blends having superior properties also is a continuing research goal. Specifically, improving optical properties, such as haze and gloss, of such polymers blends blown into film, also is an important goal of polymer research since film is often used in packaging and other applications.
It is an object of this invention to provide a process for producing a polymer composition.
It is another object of this invention to provide the polymer composition.
It is another object of this invention to provide a process for increasing the production of polymers from polymerization processes by increasing the bulk density of a narrow molecular weight distribution base polymer by incorporating a high molecular weight polymer component with the narrow molecular weight distribution base polymer to produce a polymer composition.
It is another object of this invention to provide a process for increasing the clarity of blown film produced from a narrow molecular weight distribution base polymer by incorporating a high molecular weight polymer component with the narrow molecular weight distribution base polymer to produce a polymer composition.
In accordance with one embodiment of this invention, a process for producing a polymer composition is provided. The process comprises incorporating a narrow molecular weight distribution base polymer and a high molecular weight polymer component to produce the polymer composition;
wherein the base polymer is an ethylene polymer having a Mw/Mn less than about 5 and a melt flow index from about 0.2 g/10 min to about 20 g/10 min; and
wherein the high molecular weight polymer component has a molecular weight distribution such that at least a substantial portion of its molecules have a molecular weight of greater than one million, the component being incorporated is in an amount to give about 0.1 to about 10% by weight, based on the total weight of said polymer composition, of the molecules having a molecular weight greater than one million.
These objects, and other objects, will become more apparent to those with ordinary skill in the art after reading this disclosure.
A process is provided for producing a polymer composition. The process comprises incorporating a narrow molecular weight distribution base polymer and a high molecular weight polymer component. The narrow molecular weight distribution base polymer is hereinafter referred to as a xe2x80x9cbase polymerxe2x80x9d. When the base polymer is incorporated with the high molecular weight polymer component, the bulk density of the base polymer is increased, thereby, increasing the production rate. The bulk density of the polymer composition can be increased by about 10% to about 40% over the bulk density of the base polymer. In order to achieve the bulk density increase, the high molecular weight polymer component must be incorporated with the base polymer while the base polymer is produced in a polymerization zone.
Another benefit of incorporating the base polymer and the high molecular weight polymer component is to increase the clarity of blown film produced from the base polymer. In order to achieve this clarity increase, the incorporation of the high molecular weight polymer component can be accomplished either while the base polymer is being produced in the polymerization zone or after the base polymer and high molecular weight polymer component have been produced separately. For example, the base polymer and high molecular weight polymer component can be blended together to produce the polymer composition. The haze of the polymer composition can be decreased by about 5% to as much as about 60% over the haze of the base polymer, and the gloss of the polymer composition can be increased by about 10 to about 40% over the gloss of the base polymer.
The base polymer is defined as the narrow molecular weight polymer before the high molecular weight polymer component is added to produce the polymer composition. The base polymer can be any narrow molecular weight distribution ethylene polymer, either a homopolymer or copolymer, such as, for example, ethylene-hexene copolymers. The base polymer has a Mw(weight average molecular weight)/Mn (number average molecular weight) of less than about 5.0. Preferably, Mw/Mn of the base polymer is less than about 4.0, and most preferably, Mw/Mn of the base polymer is less than 3.0.
Base polymers can be produced from any catalyst known in the art to produce narrow molecular weight distribution polymers. For example, metallocene catalysts of various types, such as described in U.S. Pat. Nos. 5,436,305; 5,610,247; and 5,627,247, herein incorporated by reference, can be used to produce the base polymer. Ziegler catalysts containing magnesium and titanium halides, such as described in U.S. Pat. Nos. 5,275,992; 5,179,178; 5,275,992; 5,237,025; 5,244,990; and 5,179,178, herein incorporated by reference, can also be used. Chromium catalysts as described for example in U.S. Pat. Nos. 3,887,494; 3,119,569; 3,900,457; 4,981,831; 4,364,842; and 4,444,965, herein incorporated by reference, also can be utilized to produce the base polymer. Preferably, the base polymer is produced from metallocene catalyst. Since these catalysts are well known to produce a narrow molecular weight distribution polymer, are very active, and often are very efficient for the incorporation of comonomer.
The base polymer can be an ethylene homopolymer or preferably, a copolymer of ethylene and at least one other alpha-olefin, such as 1-hexene, 1-butene, or 1-octene. Most preferably, the base polymer is an ethylene-hexene copolymer.
Generally, the density of the base polymer is in a range of about 0.900 g/cc to about 0.975 g/cc. Preferably, the density of the base polymer is in a range of about 0.910 g/cc to about 0.940 g/cc, and most preferably, from 0.915 g/cc to 0.93 g/cc. Generally, the base polymer has a melt flow index in a range from about 0.2 g/10 min to about 20 g/10 min. Preferably, the base polymer has a melt flow index in a range from about 0.5 g/10 min to about 10 g/10 min, and most preferably from 0.8 g/10 min to 5.0 g/10 min.
The high molecular weight polymer component can be produced from most any known catalyst system, whether the high molecular weight polymer component is produced simultaneously with the base polymer in the polymerization zone, or separately and blended later. Suitable catalysts for production of the high molecular weight polymer component include, but are not limited to, Ziegler catalysts based on titanium halides, zirconium halides, zirconium alkyls, chromium oxide catalysts, metallocene catalysts, and mixtures thereof.
The high molecular weight polymer component has a molecular weight distribution, such that, a substantial portion of its molecules have a molecular weight greater than one million. Generally, the high molecular weight polymer component being incorporated is in an amount to give about 0.1% to about 10% by weight, based on the total weight of the polymer composition, of the molecules having a molecular weight greater than one million. Preferably, the high molecular weight polymer component being incorporated is in an amount to give about 0.5% to about 5% by weight, based on the total weight of the polymer composition, of the molecules having a molecular weight greater than one million, most preferably, 1% to 3% by weight.
It is not imperative that the additional high molecular weight polymer component be pure. For example, a high molecular weight polymer component which also contains a substantial amount of polymer of molecular weight lower than one million can be incorporated into the base polymer provided it has a sufficient amount of polymer above one million in molecular weight to contribute the proper amount of high molecular weight polymer component described previously.
To achieve the increase in bulk density of the polymer composition, the high molecular weight polymer component must be incorporated with the base polymer in the polymerization zone. Any method known in the art to incorporate the high molecular weight polymer component with the base polymer in the polymerization zone can be utilized.
One method of incorporating the high molecular weight polymer component is to modify a polymerization catalyst system before it is added to the polymerization zone. For example, a second transition metal component can be added to the polymerization catalyst system which then is capable of generating simultaneously the base polymer and the high molecular weight polymer component.
A second method of incorporating the high molecular weight polymer component is to chemically modify the polymerization catalyst system while it is in the polymerization zone, such as by adding a second component which will react with a catalyst in the polymerization catalyst system to create the high molecular weight polymer component. For example, a metallocene catalyst system can be modified to include a titanium or chromium component, either before the metallocene catalyst system is introduced into the polymerization zone, or while it is in the polymerization zone. A halided, titanium-containing solid oxide compound or fluorided, chromium-containing solid oxide compound can be utilized as the titanium or chromium component.
The halided, titanium-containing solid oxide compound comprises at least one halogen, titanium, and a solid oxide compound. The halogen is at least one selected from the group consisting of chlorine, bromine, and fluorine. Generally, the solid oxide compound is selected from the group consisting of alumina, silica, aluminophosphate, aluminosilicates, aluminoborates, silica-zirconia, silica-titania, and mixtures thereof. Preferably, the solid oxide compound is silica-alumina or alumina. The solid oxide compound can be produced by any method known in the art, such as, for example, by gelling, co-gelling, impregnation of one compound onto another, and flame hydrolysis.
When silica-titania is used, the content of titania can be about 1 to about 15% by weight titanium based on the total weight of the silica-titania, preferably, about 2.5 to about 12% by weight, and most preferably, 4 to 10% by weight, with the remainder being primarily silica. The silica-titania can be produced by any method known in the art. Such processes are disclosed in U.S. Pat. Nos. 3,887,494; 3,119,569; 4,405,501; 4,436,882; 4,436,883; 4,392,990; 4,081,407; 4,152,503; 4,981,831; 2,825,721; 3,225,023; 3,226,205; 3,622,521; and 3,625,864; the entire disclosures of which are hereby incorporated by reference. The silica-titania can be made by cogellation of aqueous materials, or by cogellation in an organic or anhydrous solution, or by coating the surface of silica with a layer of titania such as, for example, by reaction of silanol groups with titanium isopropoxide followed by calcining.
Aluminophosphate can be made by any method known in the art, such as, for example, those methods disclosed in U.S. Pat. Nos. 4,364,842, 4,444,965; 4,364,855; 4,504,638; 4,364,854; 4,444,964; 4,444,962; 4,444,966; and 4,397,765; the entire disclosures of which are hereby incorporated by reference.
Silica-alumina can be made by any method known in the art. The amount of alumina in the silica-alumina can range from about 2 to about 50% by weight based on the total weight of the silica-alumina, preferably, from about 5 to about 30% by weight, and most preferably, 8 to 20% by weight. Commercial grade silica-alumina is available as MS13-110 from W. R. Grace and commercial grade alumina as Ketjen Grade B or Ketjen Grade L from Akzo Nobel.
Generally, the specific surface area of the solid oxide compound is from about 100 to about 1000 m2/g, preferably, from about 200 to about 800 m2/g, and most preferably, from 250 to 600 m2/g after calcining at 500xc2x0 C.
The specific pore volume of the solid oxide compound is typically greater than about 0.5 cm3/g, preferably, greater than about 0.8 cm3/g, and most preferably, greater than 1.0 cm3/g.
The halided, titanium-containing solid oxide compound can be produced when the solid oxide compound is contacted with at least one titanium-containing compound and at least one halogen-containing compound. The order of contacting the solid oxide compound with the titanium-containing compound and the halogen-containing compound can vary.
To produce the halided, titanium-containing solid oxide compound, at least one titanium-containing compound is contacted with the solid oxide compound by any means known in the art to produce a titanium-containing solid oxide compound. Titanium can be added to the solid oxide compound before, during, or after calcining. Generally, the amount of titanium present in the titanium-containing solid oxide compound is in a range of about 0.01 to about 10 weight percent titanium where the weight percent is based on the weight of the titanium-containing solid oxide compound. Preferably, the amount of titanium present in the titanium-containing solid oxide compound is in a range of about 0.1 to about 5 weight percent titanium based on the weight of the titanium-containing solid oxide compound. Most preferably, the amount of titanium present in the titanium-containing solid oxide compound is in a range of 0.5 to 2 weight percent titanium based on the weight of the titanium-containing solid oxide compound.
In one method of producing a titanium-containing solid oxide compound, the solid oxide compound can be contacted with an aqueous or organic solution of the titanium-containing compound before calcining. For example, the titanium can be added to the solid oxide compound by forming a slurry of the solid oxide compound in a solution of the titanium-containing compound and a suitable solvent such as alcohol or water. Particularly suitable are one to three carbon atom alcohols because of their volatility and low surface tension. Titanium alkoxides, Ti(OR)4, where R is an alkyl or aryl group having 1 to about 12 carbons, is particularly suitable as a titanium source. A suitable amount of the solution is utilized to provide the desired concentration of titanium after drying. Drying can be effected by any method known in the art. For example, said drying can be completed by suction filtration followed by evaporation, vacuum drying, spray drying, or flash drying. This method is exemplified by U.S. Pat. Nos. 4,294,724; 4,382,022; 4,402,864; 4,405,768; and 4,424,320; the entire disclosures of which are herein incorporated by reference.
In a second method, the titanium can be cogelled into the solid oxide compound when the solid oxide compound is being produced as exemplified by U.S. Pat. Nos. 3,887,494; 3,119,569; 4,405,501, and 4,436,882, the entire disclosures of which are herein incorporated by reference.
If the titanium is added before calcination, any water soluble or organic soluble titanium-containing compound is suitable that can impregnate the solid oxide compound with titanium. In a coprecipitation method, a titanium compound such as titanium halides, titanium nitrates, titanium sulfates, titanium oxalates, or alkyl titanates, for example, is incorporated with an acid or a silicate. Titanyl sulfate (TiOSO4) dissolved in sulfuric acid is a particularly suitable compound. If the titanium is deposited onto the surface of an already formed solid oxide compound, titanium halides, TiX4 where X is chloride or bromide, or alkyl titanates, Ti(OR)4 where R is an alkyl or aryl group containing 1 to about 12 carbons are preferred.
If the titanium is added during calcining, one convenient method is to vaporize a volatile titanium-containing compound, such as titanium tetrachloride or titanium tetrafluoride, or an alkyl titanate (Ti(OR)4 where R is an alkyl or aryl group containing 1 to about 12 carbons, into a gas stream used to contact the solid oxide compound.
If the titanium is added after calcining, a preferred method is to impregnate the solid oxide compound with a hydrocarbon solution of the titanium-containing compound, preferably a titanium halide or titanium alkoxyhalide, such as TiCl4, TiORCl3, Ti(OR)2Cl2, and the like, where R is an alkyl or aryl group having 1 to about 12 carbons.
Calcining is conducted at various steps in the production of the halided, titanium-containing solid oxide compound. Generally, calcining is conducted for about 1 minute to about 100 hours, preferably from about 1 hour to about 50 hours, and most preferably, from 3 to 20 hours. Generally, the calcining is conducted at a temperature in a range of about 200xc2x0 C. to about 900xc2x0 C., preferably from about 300xc2x0 C. to about 700xc2x0 C., and most preferably, from 350xc2x0 C. to 600xc2x0 C. The calcining can be conducted in any suitable atmosphere. Generally, the calcining can be completed in an inert atmosphere. Alternatively, the calcining can be completed in an oxidizing atmosphere, such as, oxygen or air, or a reducing atmosphere, such as, hydrogen or carbon monoxide.
To produce the halided, titanium-containing solid oxide compound, the solid oxide compound is also contacted with at least one halogen-containing compound. The halogen-containing compound is at least one selected from the group consisting of chlorine-containing compounds, bromine-containing compounds, and fluorine-containing compounds. The halogen-containing compound can be in a liquid phase, or preferably, a vapor phase. Optionally, the solid oxide compound can be calcined at about 100xc2x0 C. to about 900xc2x0 C. before being contacted with the halogen-containing compound.
Any method of fluoriding the solid oxide compound known in the art can be used in this invention. A common method is to impregnate the solid oxide compound with an aqueous solution of a fluoride-containing salt before calcining, such as ammonium fluoride [NH4F], ammonium bifluoride [NH4HF2], hydrofluoric acid [HF], ammonium silicofluoride [(NH4)2SiF6], ammonium fluoroborate [NH4BF4], ammonium fluorophosphate [NH4PF6], and mixtures thereof.
In a second method, the fluorine-containing compound can be dissolved into an organic compound, such as an alcohol, and added to the solid oxide compound before calcining to minimize shrinkage of pores during drying. Drying can be accomplished by an method known in the art, such as, for example, vacuum drying, spray drying, flashing drying, and the like.
In a third method, the fluorine-containing compound can be incorporated into the gel formed when producing a solid oxide compound by adding it to at least one of the solutions before gellation. Alternatively, the fluorine-containing compound can be added to the gel before drying. Gellation methods to produce a solid oxide compound were discussed previously in this disclosure.
In a fourth method, the fluorine-containing compound can be added during calcining. In this technique, the fluorine-containing compound is vaporized into the gas stream used to fluidize the solid oxide compound so that it is fluorided from the gas phase. In addition to some of the fluorine-containing compounds described previously, volatile organic fluorides can be used at temperatures above their decomposition points, or at temperatures high enough to cause reaction. For example, perfluorohexane, perfluorobenzene, trifluoroacetic acid, trifluoroacetic anhydride, hexafluoroacetylacetonate, and mixtures thereof can be vaporized and contacted with the solid oxide compound at about 300xc2x0 C. to about 600xc2x0 C. in air nitrogen. Inorganic fluorine-containing compounds can also be used, such as hydrogen fluoride or even elemental fluorine.
The amount of fluorine present on the halided, titanium-containing solid oxide compound is about 2 to about 50 weight percent fluorine based on the weight of the halided, titanium-containing solid oxide compound before calcining or the amount added to a precalcined solid oxide compound. Preferably, it is about 3 to about 25 weight percent, and most preferably, it is 4 to 20 weight percent fluorine based on the weight of the halided, titanium-containing solid oxide compound before calcining or the amount added to a precalcined solid oxide compound.
Any method of contacting the solid oxide compound with the chlorine-containing compound or the bromine-containing compound known in the art can be used in this invention. Generally, the contacting is conducted during or after calcining, preferably during calcining. Any suitable chlorine-containing compound or bromine-containing compound that can deposit chlorine or bromine or both on the solid oxide compound can be used. Suitable chlorine-containing compounds and bromine-containing compound include volatile or liquid organic chloride or bromide compounds and inorganic chloride or bromide compounds. Organic chloride or bromide compounds can be selected from the group consisting of carbon tetrachloride, chloroform, dichloroethane, hexachlorobenzene, trichloroacetic acid, bromoform, dibromomethane, perbromopropane, phosgene, and mixtures thereof. Inorganic chloride or bromide compounds can be selected from the group consisting of gaseous hydrogen chloride, silicon tetrachloride, tin tetrachloride, titanium tetrachloride, aluminum trichloride, boron trichloride, thionyl chloride, sulfuryl chloride, hydrogen bromide, boron tribromide, silicon tetrabromide, and mixtures thereof. Additionally, chlorine and bromine gas can be used. Optionally, a fluorine-containing compound can also be included when contacting the zirconium-containing solid oxide compound with the chlorine-containing compound or bromine-containing compound to achieve higher activity in some cases.
If an inorganic chlorine-containing compound or bromine-containing compound is used, such as titanium tetrachloride, aluminum trichloride, or boron trichloride, it can also be possible to achieve the chloriding or bromiding after calcining, either by vapor phase deposition or even by using an anhydrous solvent.
The amount of chlorine or bromine used can be from about 0.01 to about 10 times the weight of the halided, titanium-containing solid oxide compound before calcining or the amount added to a precalcined solid oxide compound, preferably it is from about 0.05 to about 5 times, most preferably from 0.05 to 1 times the weight of the halided, titanium-containing solid oxide compound before calcining or the amount added to a precalcined solid oxide compound.
Generally, the solid oxide compound is contacted with the chlorine-containing compound or bromine-containing compound at a temperature in the range of about 25xc2x0 C. to about 1000xc2x0 C., preferably from about 200xc2x0 C. to 700xc2x0 C., and most preferably from 300xc2x0 C. to 600xc2x0 C.
In another embodiment of this invention, an additional compound can be added to the halided, titanium-containing solid oxide compound to enhance the activity of the organometal compound. For example, an additional metal, such as, zinc, silver, copper, antimony, gallium, tin, nickel, tungsten, and mixtures thereof, can be added by contacting the halided, titanium-containing solid oxide compound with a metal-containing compound. This is especially useful if the solid oxide compound is to be chlorided during calcining. When used, these metals are added in an amount of about 0.01 to about 10 millimoles per gram of halided, titanium-containing solid oxide compound, preferably about 0.1 to about 5 millimoles per gram, and most preferably from 0.5 to 3 millimoles of metal per gram of halided, titanium-containing solid oxide compound.
Preferably, magnesium is added to the halided, titanium-containing solid oxide compound to increase the activity of the titanium component of the catalyst composition by contacting the halided, titanium-containing solid oxide compound with a magnesium-containing compound. The amount of magnesium used can be from about 0.01 to about 10 millimoles per gram of halided, titanium-containing solid oxide compound, preferably from about 0.1 to about 5 millimoles per gram, most preferably from 0.1 to 1 millimoles per gram of halided, titanium-containing solid oxide compound. If magnesium is added, it can be added before or after calcining. One preferred method of adding magnesium is to contact an organomagnesium compound in a hydrocarbon solution with the halided, titanium-containing solid oxide compound. Examples of such compounds include, but are not limited to, dialkyl magnesium, alkyl magnesium halide, magnesium alkoxide or aryloxides, and the like.
The fluorided, chromium-containing solid oxide compound comprises fluorine, chromium, and a solid oxide compound. The solid oxide compounds discussed previously can be utilized to produce the fluorided, chromium-containing solid oxide compound. The fluorine can be added to the solid oxide compound as discussed previously for the halided, titanium-containing solid oxide compound. The chromium can be added to the solid oxide compound as discussed previously for titanium. Examples of chromium-containing compounds include, but are not limited to, chromium trioxide (CrO3), ammonium chromate ((NH4)2CrO4), ammonium dichromate ((NH4)2Cr2O7), chromic acetate (Cr(C2H3O3), chromic nitrate (Cr(NO3)3), chromous chloride (CrCl2), bis-benzene chromium(0) ((C6H6)2Cr), chromocene ((C5H5)2Cr), and mixtures thereof. The amount of chromium present is in the range of about 0.01 to about 10% by weight, preferably, about 0.5 to about 5% by weight, and most preferably, from 0.8% to 3% by weight, where the weight percents are based on the weight of the chromium-containing solid oxide compound before calcining.
A third method to incorporate the high molecular weight polymer component is to produce a metallocene catalyst system comprising two metallocene components with a first metallocene component producing the base polymer and a second metallocene component producing the high molecular weight polymer component. Again, this can be accomplished before introduction into the polymerization zone or while in the polymerization zone.
To achieve improvements in the clarity of blown films made from the base polymer, the high molecular weight polymer component can be incorporated as described previously through catalyst system modification, or it can also be incorporated after production in the polymerization zone, such as, by melt blending the base polymer and the high molecular weight polymer component together. Preferably, the clarity improvement is obtained through catalyst modification since no blending is required.
Polymerization can be carried out in any manner known in the art, such as, for example, gas phase, solution or slurry conditions, to effect polymerization. Any polymerization zone known in the art to produce ethylene polymers can be utilized. For example, a stirred reactor can be utilized for a batch process, or the reaction can be carried out continuously in a loop reactor or in a continuous stirred reactor. Processes that can polymerize monomers into polymers using the catalyst systems of this invention are known in the art, such as, for example, slurry polymerization, gas phase polymerization, solution polymerization, and multi-reactor combinations thereof.
A preferred polymerization technique is that which is referred to as a particle form, or slurry process, wherein the temperature is kept below the temperature at which the polymer swells or goes into solution. A loop reactor is particularly preferred. Such polymerization techniques are well known in the art and are disclosed, for instance, in Norwood, U.S. Pat. No. 3,248,179, the disclosure of which is hereby incorporated by reference. Furthermore, it is even more preferred to use isobutane as a diluent in a slurry polymerization. Examples of such technology can be found in U.S. Pat. Nos. 4,424,341; 4,501,885; 4,613,484; 4,737,280; and 5,597,892; the entire disclosures of which are hereby incorporated by reference.
The preferred temperature in the particle form process is within a range of about 185xc2x0 F. to about 230xc2x0 F. (about 85xc2x0 C. to about 110xc2x0 C.), although higher or lower temperatures can be used. Two preferred polymerization methods for the slurry process are those employing a loop reactor of the type disclosed in Norwood and those utilizing a plurality of stirred reactors either in series, parallel or combinations thereof wherein the reaction conditions can be different in the different reactors.
Monomers useful in this invention are unsaturated hydrocarbons having from 2 to about 20 carbon atoms. Currently, it is preferred when the monomer is selected from the group consisting of ethylene, propylene, 1-butene, 3-methyl-1-butene, 1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-hexene, 3-ethyl-1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, and mixtures thereof. However, when a homopolymer is desired, it is most preferred to use ethylene, or propylene, as the monomer. Additionally, when a copolymer is desired, it is most preferred to use ethylene and hexene as the monomers. The polymer density can be controlled by varying the comonomer to monomer ratio in the polymerization zone.
The molecular weight of the polymer composition can be controlled by various means known in the art, such as, for example, adjusting the temperature (higher temperature giving lower molecular weight), introducing or varying the amount of hydrogen to alter the molecular weight, and varying the catalyst components in the catalyst system.